A hydraulic machine of this kind is, for example, known from EP 0 959 248 A2. During motor operation, the valve arrangement supplies the expanding pressure chambers with pressurised hydraulic fluid from the hydraulic connection, whereas the contracting chambers are connected with the low-pressure connection via the valve arrangement, so that the hydraulic fluid from the contracting pressure chambers can be displaced. When the machine is operated as a pump, the valve arrangement connects the contracting pressure chambers with the high-pressure connection and the expanding chambers with the low-pressure connection.
In such machines, it is important that the supply to the individual pressure chambers is controlled relatively accurately by the valve arrangement. This is particularly crucial, when a transition from an expansion phase to a contraction phase occurs in a pressure chamber, that is, when the pressure chamber has reached its maximum volume or its minimum volume.
The known machine has a secondary commutation, which ensures that any pressure chamber has a connection outside the valve arrangement to any neighbouring pressure chambers until shortly before it reaches a minimum or a maximum volume. At the instant of the commutation it is ensured that there is no connection between the pressure chamber with maximum or minimum volume and the corresponding neighbouring pressure chambers. Thus, a stable operation with low speeds and high pressures is achieved.
A hydraulic machine as mentioned in the introduction, which is also called a gerotor machine, drives a valve element of the valve arrangement, which influences the correct positioning of the supply of the pressure chambers, via a cardan shaft or via another coupling arrangement. For several reasons, this may cause a small angle displacement between the valve element and the gear wheel that drives the valve element. Under certain circumstances, this angle displacement may cause that the pressure chambers are not connected with the corresponding supply connections in the correct position. This causes an instable operation, and in the extreme it may even lead to a damaging of the machine.
The invention is based on the task of achieving a stable operation, particularly with low speeds under high loads.